[llvm][DebugInfo][test] Add LLVM tests for Objective-C property debug-info

The IR->DWARF pipeline was not properly tested before. This patch adds a
test to generate DWARF for various `DIObjCProperty` constructions.

This caught a couple of bugs:
1. The `DW_AT_APPLE_property_getter` and `DW_AT_APPLE_property_setter`
   properties were emitted the wrong way around.
2. The `DW_TAG_member` ivars were not linking back to the property that
   they back.

These will be fixed in follow-up patches.

Author: Michael137

llvm/test/DebugInfo/Generic/objc-property.ll

@@ -86,4 +86,3 @@
 !30 = !DISubprogram(name: "-[Foo setAutoSynthProp:]", scope: !5, file: !3, line: 5, type: !25, scopeLine: 5, flags: DIFlagArtificial | DIFlagPrototyped, spFlags: DISPFlagLocalToUnit)
 !31 = !DISubprogram(name: "-[Foo setCustomGetterProp:]", scope: !5, file: !3, line: 7, type: !25, scopeLine: 7, flags: DIFlagArtificial | DIFlagPrototyped, spFlags: DISPFlagLocalToUnit)
 !32 = !DISubprogram(name: "-[Foo customSetterProp]", scope: !5, file: !3, line: 8, type: !18, scopeLine: 8, flags: DIFlagArtificial | DIFlagPrototyped, spFlags: DISPFlagLocalToUnit)
-